It is known that internal combustion engines comprise a lubrication circuit suitable for lubricating the rotating or sliding components of the engine. This lubrication circuit generally comprises an oil pump driven by the engine, which draws lubricating oil from an oil sump and delivers it under pressure through a main oil gallery that is realized in the cylinder block. The main oil gallery is connected via respective channels with a plurality of exit holes for lubricating crankshaft bearings (main bearings and big-end bearings), camshaft bearings operating the valves, tappets, and the like, from which the lubricating oil finally returns into the oil sump.
In order to reduce polluting emission and fuel consumption, most recent internal combustion engines are provided with a variable displacement oil pump (VDOP), which is controlled by an engine control unit (ECU) to vary its own displacement based on the engine operating conditions. A known VDOP comprises an external casing provided with an oil inlet and with an oil outlet, an operative chamber enclosed inside the casing and communicating with the oil inlet and the oil outlet, and a rotor, having a plurality of radial blades sliding in respective slots of the rotor, which is accommodated inside the operative chamber for drawing the oil from the oil inlet and pumping it towards the oil outlet.
The operative chamber is partially delimited by an annular element, which is accommodated inside the external casing to eccentrically enclose the rotor, and which can be moved in different operating positions to vary the eccentricity of the rotor and thus the displacement of the pump. The movements of the annular element are caused by the pressure of the lubricating oil contained into two control chambers, namely a primary control chamber and a secondary control chamber, which are defined inside the VDOP external casing, separated from the operative chamber by the said annular element.
The pressure of the lubricating oil in the control chambers shoves the annular element towards a position of minimum eccentricity, in contrast with a spring. The control chambers communicates with a feedback channel realized in the VDOP external casing, which is connectable with the main oil gallery of the engine lubrication circuit and thus with the oil outlet of the VDOP.
While the feedback channel is always in communication with the primary control chamber, an electrically driven control valve is provided for selectively open and close the communication between the feedback channel and the secondary control chamber. In greater detail, the control valve is a three way valve provided for selectively put the secondary control chamber in communication with the feedback channel or alternatively with a discharging channel leading in the oil sump. In this way, when the second control chamber communicates with the oil sump, the position of the annular element of the VDOP depends on the force exerted by the pressure of the lubricating oil in the primary control chamber only, so that the annular element tends to stay nearby the maximum eccentricity position, but when the second control chamber communicates with the feedback channel, the position of the annular element of the VDOP depends on the force exerted by the pressure of the lubricating oil in both the control chambers, so that the annular element suddenly moves towards and tends to stay nearby a position of reduced eccentricity.
The above named control valve is conventionally accommodated in a dedicated seat which is directly realized in the external casing of the VDOP, in order to provide an integrated assembly that can be managed as a whole. However, this solution considerably affects the layout of the lubrication circuit, because the VDOP must necessarily be located in a position where the electric connector of the control valve can be safely and easily wired to the ECU, where the wiring that connects the control valve with the ECU is possibly not wetted by the engine oil, and where the control valve is easily accessible in case of replacement and/or maintenance.
In view of the above, at least one object to solve the above mentioned drawback, allowing the VDOP to be located where conventionally it could not be located due to the control valve. At least another object is to achieve this goal with a simple, rational, and rather inexpensive solution. In addition, other objects, desirable features and characteristics will become apparent from the subsequent summary and detailed description, and the appended claims, taken in conjunction with the accompanying drawings and this background.